Communication apparatus and control method therefor

ABSTRACT

This invention provides a communication apparatus, which suppresses abrupt changes of a current and voltage generated in a communication line upon connecting an external telephone to the communication line, and a control method thereof. To accomplish this, in a communication apparatus of this invention, when an off-hook state of an external telephone is detected upon connecting the external telephone to a communication line, an SOC captures a line using a first line capture means having an impedance lower than the external telephone side, and then switches an H-relay to connect the external telephone to the communication line. Furthermore, the SOC temporarily switches a line capture state to a second line capture means having an impedance higher than the first line capture means after the H-relay is switched and before the line is released.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a communication apparatus and controlmethod therefor.

2. Description of the Related Art

Conventionally, communication apparatuses such as facsimile (FAX)apparatuses are available which can connect, to a communication linesuch as a telephone line, not only a FAX communication unit for a FAXcommunication (modem) but also a telephone for a voice communication.For example, Japanese Patent Laid-Open No. 05-007273 discloses a FAXapparatus which can selectively connect a data communication unit usedto make a data communication and a telephone used to make a voicecommunication to a communication line. When this FAX apparatus switchesthe data communication unit to the telephone and connects it to thecommunication line, the data communication unit and telephone areconnected to the communication line in parallel to each other, so as tosupply a line current to the telephone, thereby setting the telephone ina voice communication ready state before switching connection to it.

Some of such conventional FAX apparatuses are connected to a publicbranch exchange (PBX), but most of them are connected to a publicswitched telephone network (PSTN). Strict managements are made for FAXapparatuses connected to the PSTN and apparatuses introduced asswitching equipments on the PSTN side, so that these apparatuses meetpredetermined technical criteria.

On the other hand, a technique called “VoIP” (Voice over InternetProtocol) which exchanges voice data using an IP network having abroadband transmission path such as a Digital Subscriber Line (DSL) oroptical line has prevailed.

When the user connects the aforementioned communication apparatus forthe PSTN (a FAX apparatus will be exemplified below) to the IP network,and makes a voice communication by a telephone connected to thecommunication apparatus using the VoIP, he or she encounters thefollowing problem. For example, an adapter which serves as an interfaceused to convert a voice signal output from the apparatus into a signalhaving a format suited to the IP network is required. This adapternormally not only sends the input voice signal onto the IP network, butalso specifies a communication destination by detecting an input dialpulse signal.

Since the adapter connected to the FAX apparatus is not connected to thePSTN, it is not required to meet the predetermined technical criteriarequired for the PSTN connection. For this reason, such adapter mayoften erroneously detect, as a dial pulse signal, a weak current orvoltage change having a short time width at a level as low as it cannotbe detected as a regular dial pulse signal according to the criteria forthe PSTN.

More specifically, in the communication apparatus, a weak current orvoltage change having a very short time width, which is caused uponswitching of an internal relay or an off-hook operation of theexternally attached telephone, may often be erroneously detected by theaforementioned adapter as a dial pulse signal. In this case, theapparatus cannot dial to a correct destination based on the dial pulsesignal from the telephone.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of theaforementioned problems, and provides a communication apparatus whichaims to suppress abrupt changes of a current and voltage generated in acommunication line upon connecting an external telephone to thecommunication line.

One aspect of the present invention provides a communication apparatus,which comprises a connection unit that an external telephone isconnected to, a switching unit that switches between a connection statein which the external telephone is connected to a line and adisconnection state in which the external telephone is disconnected fromthe line, a detection unit that detects an off-hook state of theexternal telephone, and a network control unit that is connected to theline in parallel to the external telephone, and controls a capture stateof the line, the apparatus comprising: a first capture control unit thatcaptures, when the detection unit detects the off-hook state of theexternal telephone in the disconnection state, the line using a firstline capture unit, an impedance of which is lower than the externaltelephone side, and which is included in the network control unit; aconnection control unit that connects the external telephone to the lineby switching the switching unit to the connection state after the firstline capture unit captures the line; a second capture control unit thatcaptures the line by switching to a second line capture unit, animpedance of which is higher than the first line capture unit and whichis included in the network control unit, after the external telephone isconnected to the line; and a line release unit that releases the capturestate of the line by the second line capture unit after the second linecapture unit captures the line.

Another aspect of the present invention provides a communicationapparatus, which comprises a connection unit that an external telephoneis connected to, a switching unit that switches between a connectionstate in which the external telephone is connected to a line and adisconnection state in which the external telephone is disconnected fromthe line, a detection unit that detects an off-hook state of theexternal telephone, and a network control unit that is connected to theline in parallel to the external telephone, and controls a capture stateof the line, the apparatus comprising: a first capture control unit thatsets, when the detection unit detects the off-hook state of the externaltelephone in the disconnection state, an impedance of a line captureunit included in the network control unit to be a first impedance lowerthan the external telephone side, and captures the line using the linecapture unit; a connection control unit that connects the externaltelephone to the line by switching the switching unit to the connectionstate after the line capture unit of the first impedance captures theline; a second capture control unit that changes the impedance of theline capture unit to a second impedance higher than the first impedance,and captures the line using the line capture unit, after the externaltelephone is connected to the line; and a line release unit thatreleases the capture state of the line by the line capture unit afterthe line capture unit of the second impedance captures the line.

Still another aspect of the present invention provides a control methodof a communication apparatus, which comprises a connection unit that anexternal telephone is connected to, a switching unit that switchesbetween a connection state in which the external telephone is connectedto a line and a disconnection state in which the external telephone isdisconnected from the line, a detection unit that detects an off-hookstate of the external telephone, and a network control unit that isconnected to the line in parallel to the external telephone, andcontrols a capture state of the line, the method comprising: controllinga first capture control unit to capture, when the detection unit detectsthe off-hook state of the external telephone in the disconnection state,the line using a first line capture unit, an impedance of which is lowerthan the external telephone side, and which is included in the networkcontrol unit; controlling a connection control unit to connect theexternal telephone to the line by switching the switching unit to theconnection state after the first line capture unit captures the line;controlling a second capture control unit to capture the line byswitching to a second line capture unit, an impedance of which is higherthan the first line capture unit and which is included in the networkcontrol unit, after the external telephone is connected to the line; andcontrolling a line release unit to release the capture state of the lineby the second line capture unit after the second line capture unitcaptures the line.

Yet another aspect of the present invention provides a control method ofa communication apparatus, which comprises a connection unit that anexternal telephone is connected to, a switching unit that switchesbetween a connection state in which the external telephone is connectedto a line and a disconnection state in which the external telephone isdisconnected from the line, a detection unit that detects an off-hookstate of the external telephone, and a network control unit that isconnected to the line in parallel to the external telephone, andcontrols a capture state of the line, the method comprising: controllinga first capture control unit to set, when the detection unit detects theoff-hook state of the external telephone in the disconnection state, animpedance of a line capture unit included in the network control unit tobe a first impedance lower than the external telephone side, and tocapture the line using the line capture unit; controlling a connectioncontrol unit to connect the external telephone to the line by switchingthe switching unit to the connection state after the line capture unitof the first impedance captures the line; controlling a second capturecontrol unit to change the impedance of the line capture unit to asecond impedance higher than the first impedance, and to capture theline using the line capture unit, after the external telephone isconnected to the line; and controlling a line release unit to releasethe capture state of the line by the line capture unit after the linecapture unit of the second impedance captures the line.

An advantage of the claimed invention is that it can provide acommunication apparatus which suppresses abrupt changes of a current andvoltage generated in a communication line upon connecting an externaltelephone to the communication line.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments (with reference to theattached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an example of the block arrangement ofa FAX apparatus 100 according to an embodiment of the present invention;

FIG. 2 is a block diagram showing an example of the block arrangementassociated with a modification of the FAX apparatus 100 according to theembodiment of the present invention;

FIGS. 3A and 3B are flowcharts showing the operation sequence based on ano-ringing FAX mode of the FAX apparatus 100 according to the embodimentof the present invention;

FIG. 4 is a flowchart that, together with FIG. 3B shows the operationsequence based on an F/T mode (FAX/TELEPHONE) of the FAX apparatus 100according to the embodiment of the present invention;

FIG. 5 is a timing chart showing the operation timings based on theno-ringing FAX mode of the FAX apparatus 100 according to the embodimentof the present invention;

FIG. 6 is a timing chart showing the operation timings based on the F/Tmode of the FAX apparatus 100 according to the embodiment of the presentinvention;

FIG. 7 is a block diagram showing an example of the block arrangement ofa FAX apparatus 700 according to a third modification of the presentinvention; and

FIG. 8 is a block diagram showing an example of the block arrangement ofan NCU (Network Control Unit) 701 in the FAX apparatus 700 according tothe third modification of the present invention.

DESCRIPTION OF THE EMBODIMENTS

An embodiment of the present invention will be described hereinafter.The technical scope of the present invention is not limited by thefollowing embodiment.

<Overall Arrangement of FAX Apparatus>

The block arrangement of a communication apparatus (a FAX apparatus willbe exemplified below) 100 according to an embodiment of the presentinvention will be described below with reference to FIG. 1. ASystem-On-Chip (SOC) 101 controls the overall system of the FAXapparatus 100. A CPU (not shown) in the FAX apparatus 100 is mounted onthe SOC 101. A memory 140 connected to the SOC 101 is a main storagedevice, and serves as a system work memory of the CPU of the SOC 101,and a memory for storing control programs required to implementprocesses shown in FIGS. 3A, 3B and 4. The memory 140 also serves as amemory used to temporarily store image data and various kinds ofinformation in, e.g., a FAX sending or receiving operation.

To the SOC 101, an operation panel 118, reading unit 121, recording unit122, and interface (IF) unit 123 are connected. The operation panel 118includes a display 119 and keyboard set 120, which serve as a userinterface. The display 119 displays states and menus of the apparatus.The keyboard set 120 includes a keyboard such as buttons and a ten-keypad which accept various instructions input from the user. The readingunit 121 reads an image from a document, and generates image data. Thegenerated image data may be FAX-sent to a partner apparatus via acommunication line 130, or may be stored and saved in the recording unit122. The interface (IF) unit 123 serves as an interface when variousinformation devices are externally connected.

A modem 102 is a modulator/demodulator, which is connected to the SOC101, and operates under the control of the SOC 101. The modem 102executes modulation processing using image data to be FAX-sent, which isread by the reading unit 121, and demodulation processing of a signalreceived via the communication line 130. The modem 102 is connected toan SDAA (Silicon Data Access Arrangement) 104 via an insulating element103.

The SDAA 104 is an example of a network control unit, and is asemiconductor NCU (Network Control Unit). The SDAA 104 is a networkcontrol device, which is connected to the communication line 130, andserves as an interface between the FAX apparatus 100 and external publicline (communication line) 130. Upon making a communication with apartner apparatus via the communication line 130, the SDAA 104 controlsa line connection (capture) state. To the communication line 130, atelephone 128 which is externally attached to the FAX apparatus 100 viaa connection terminal (connection unit) 129 is also connected. Thetelephone 128 is connected to the communication line 130 via theconnection terminal 129 and an H-relay 110, and the SDAA 104 isconnected to the communication line 130 in parallel to the telephone128. The SDAA 104 not only captures a line to control a communicationupon making a FAX-sending/receiving operation, but also controls a linecapture state when the telephone 128 is used to make a voicecommunication with a partner apparatus via the communication line 130.The SDAA 104 executes these control operations under the control of theSOC 101.

The SDAA 104 includes three line capture units, i.e., line capture units1 to 3 (line capture units 105, 106 and 107). As will be describedlater, the SDAA 104 selects one of these line capture units and controlsa line capture state using the selected unit under the control of theSOC 101. Note that the line capture units 1 to 3 are respectivelyexamples of first, second, and third line capture units. These linecapture units respectively have DC characteristics of differentimpedances. The line capture unit 1 has an impedance viewed from thecommunication line 130 lower than the telephone 128 side, and has, forexample, DC characteristics of about 150 Ω (low impedance) with respectto a current of 20 mA. On the other hand, the line capture unit 2 has animpedance higher than the line capture unit 1, and has, for example, DCcharacteristics of about 600 Ω (high impedance) with respect to acurrent of 20 mA. These line capture units 1 and 2 are used uponcapturing a line so as to connect the telephone 128 to the communicationline 130.

The line capture unit 3 is used when the SDAA 104 makes a communicationwith a partner apparatus via the communication line 130. For thispurpose, the line capture unit 3 has an impedance suitable for use in acommunication, i.e., that which is higher than the line capture unit 1and is lower than the line capture unit 2. For example, the line captureunit 3 has DC characteristics of about 300 Ω (middle impedance) withrespect to a current of 20 mA.

A CI (Call Indicator) detection circuit 108 is connected to thecommunication line 130, and detects a calling signal (to be referred toas a “CI signal” hereinafter) received from the communication line. Upondetection of a CI signal from the communication line, the CI detectioncircuit 108 sends a CI detection signal 109 indicating that detection tothe SOC 101. The SOC 101 can check based on the CI detection signal 109whether or not to receive a CI signal from the communication line.

The H-relay 110 is a circuit used to connect the external telephone 128connected via a hook detection circuit 117 to either a line feedingcircuit 112 or the communication line 130. The H-relay 110 is an exampleof a switching unit that switches between a connection state in whichthe external telephone 128 is connected to the communication line 130,and a disconnection state in which the telephone 128 is disconnectedfrom the communication line 130, and is connected to the communicationline 130, but via the line feeding circuit. If the external telephone128 is connected to the communication line 130, this does notnecessarily mean that a signal/current is transmitted from the line toeh external telephone if the signal/current is preferring to betransmitted via the SDAA 104, for example because the impedance of theSDAA 104 is lower than that of the external telephone. Also, the H-relay110 is controlled by the SOC 101 using an H-relay driving signal 111.Note that when the H-relay 110 is connected, as shown in FIG. 1, the FAXapparatus 100 is set in a state in which the external telephone rings inresponse to an incoming call.

The line feeding circuit 112 is a circuit which supplies a current fromthe communication line to the hook detection circuit 117. The linefeeding circuit 112 supplies a current to the hook detection circuit 117based on a line current fed from the communication line 130. The linefeeding circuit 112 internally switches between connection to anddisconnection from the communication line 130 under the control of theSOC 101 using a line feeding circuit connection signal 113.

The hook detection circuit 117 is an example of a detection unit, and isa circuit which is connected to the telephone 128 and detects anoff-hook or on-hook state of the telephone 128. The hook detectioncircuit 117 transmits an off-hook or on-hook detection result of thetelephone 128 to the SOC 101 using a hook detection signal 114. The SOC101 can determine a hook state of the telephone 128 based on the hookdetection signal 114. The hook detection circuit 117 detects a currentthat flows to the telephone 128 in both a case in which the telephone128 is connected directly to the communication line 130 by the H-relay110 and a case in which it is connected to the communication line 130via the line feeding circuit 112. Then, an on-hook or off-hook state ofthe telephone 128 is detected.

A pseudo CI output circuit 116 is a circuit which outputs a pseudo CIsignal to the telephone 128. The pseudo CI signal is a signal to be sentto the telephone 128 in a state disconnected from a line so as to causethe telephone 128 to ring upon reception of a CI signal from a partnerapparatus via the communication line 130. The pseudo CI output circuit116 outputs the pseudo CI signal to the telephone 128 in response to anoutput instruction based on a pseudo CI driving signal 115 from the SOC101.

In this embodiment, the FAX apparatus 100 is connected to a VoIP adapter124 via the communication line 130. The VoIP adapter 124 applies PCM(pulse-code modulation) encoding to a FAX or telephone sending signalhaving a voice-band frequency ranging from 300 to 3400 Hz, and sends thesignal onto the IP network using a protocol such as SIP (SessionInitiation Protocol). In this embodiment, for example, the output signalfrom the VoIP adapter 124 is sent onto an IP network of an optical linenetwork 127 via a broadband router 125 and line terminating device 126.The VoIP adapter 124 converts a signal received from the optical linenetwork 127 into a FAX or telephone signal having a voice-band frequencyranging from 300 to 3400 Hz. The VoIP adapter 124 sends the convertedsignal to the FAX apparatus 100 via the communication line 130. Also,the VoIP adapter 124 has a function of recognizing dial pulses from aninput signal, or recognizing hooking in the telephone 128 externallyattached to the FAX apparatus 100.

The FAX apparatus 100 with the aforementioned arrangement has variousoperation modes. This embodiment will explain a no-ringing FAX mode andF/T mode (FAX/TEL switching mode). In either operation mode, as will bedescribed later, the telephone 128 is set in a disconnection statedisconnected in advance from the line by the H-relay 110. The no-ringingFAX mode is an operation mode which allows FAX reception without causingthe telephone 128 to ring in response to a CI signal when the CIdetection circuit 108 detects reception of the CI signal. The F/T modeis an operation mode in which the SOC 101 determines whether a source isa telephone or FAX apparatus when the CI detection circuit 108 detectsreception of a CI signal. In this mode, when the source is a telephone,the SOC 101 controls the telephone 128 to ring. When the source is a FAXapparatus, the SOC 101 controls to execute FAX reception.

The FAX apparatus 100 has a function of connecting the telephone 128 tothe communication line 130 upon detection of an off-hook state of thetelephone 128 in the no-ringing FAX mode. Thus, the FAX apparatus 100provides a voice communication function using the telephone 128 to theuser. However, upon disconnecting the line feeding circuit 112 from thecommunication line 130 and upon switching the H-relay 110, an impedanceviewed from the communication line 130 becomes unstable. In this case,when the impedance changes to a low impedance and then quickly changesto a high impedance, the VoIP adapter 124 connected to the communicationline 130 might erroneously recognize changes of a current and voltagegenerated in the communication line 130 due to the impedance changes asa dial pulse. For example, when the impedance changes to a low impedanceto capture a line, then changes to a high impedance, and then returns toa low impedance, the VoIP adapter 124 erroneously recognizes suchchanges as a dial pulse “1”. In this case, when the user inputs a dialpulse signal from the telephone 128 after the line is captured by theSDAA 104, the VoIP adapter 124 recognizes that dial pulse signal as thatwith a prefix “1”, and the line is connected to a destination having awrong telephone number.

Hence, in order to cope with this problem, the FAX apparatus 100according to this embodiment executes an operation for suppressingabrupt changes of a current and voltage generated in the communicationline upon connecting the external telephone to the communication line.More specifically, when the line feeding circuit 112 is disconnectedfrom the communication line 130, and when the H-relay 110 is switched,the SDAA 104 captures a line using the line capture unit 1 having the DCcharacteristics of an impedance lower than the telephone 128 side whenviewed from the communication line 130. This prevents the impedanceviewed from the communication line 130 from becoming a high impedance(which could be mistaken for a dial pulse) because the communicationline 130 has been able to follow the lower impedance route of the SDAA104 rather than the higher impedance route of the external telephone.After that, the H-relay 110 connects the telephone 128 to thecommunication line 130, and the line capture state by the SDAA 104 isreleased in order that a line current is supplied to the telephone 128side, thereby connecting the telephone 128 to the line 130.

Depending on the telephone 128 externally connected to the FAX apparatus100, an impedance may become unstable when the telephone 128 isconnected to the communication line 130, and a line current flows intothe telephone 128. In this case, when the impedance temporarily changesin the external telephone, as described above, the VoIP adapter 124 mayerroneously recognize changes of a current and voltage caused by thoseimpedance changes as a dial pulse.

Hence, in the FAX apparatus 100 according to this embodiment, startingwith the SDAA 104 in a line capture state by using the line capture unit1 105, the SDAA 104 temporarily switches the line capture state to theline capture unit 2 106 without immediately releasing the line. The linecapture unit 2 has a higher impedance than the line capture unit 1. TheFAX apparatus 100 releases the line after then, thus graduallyincreasing a current amount flowing into the telephone 128. As a result,the impedance on the telephone 128 side can be prevented from becomingunstable, and the VoIP adapter 124 connected to the FAX apparatus 100can be prevented from erroneously recognizing a dial pulse.

<Operation in No-ringing FAX Mode>

The operation sequence executed when the external telephone 128 is setin an off-hook state in the FAX apparatus 100 during an operation in theno-ringing FAX mode will be described below with reference to FIGS. 3Aand 3B. The flowcharts shown in FIGS. 3A and 3B are implemented when theCPU of the SOC 101 executes a program in the memory 140. Together withthe operation sequence, operation timings will also be described withreference to FIG. 5. FIG. 5 shows a state 501 of the hook detectionsignal 114, a state 502 of the SDAA 104, a state 503 of the H-relay 110,and a state 504 of the line feeding circuit 112.

When the FAX apparatus 100 shifts to the no-ringing FAX mode, the SOC101 connects the H-relay 110 to the line feeding circuit 112 side usingthe H-relay driving signal 111 in step S301. In step S302, the SOC 101connects the line feeding circuit 112 to the communication line 130using a line feeding circuit connection signal 113. Thus, a line currentfrom the communication line 130 is supplied to the hook detectioncircuit 117.

In the FAX apparatus 100 in the no-ringing FAX mode, the SOC 101determines in step S303 whether or not the hook detection circuit 117detects an off-hook state of the telephone 128. When the hook detectioncircuit 117 detects an off-hook state of the telephone 128 (511 in FIG.5), it sends the hook detection signal 114 to the SOC 101 to inform itof detection of the off-hook state. If the SOC 101 determines, based onthe hook detection signal 114, that no off-hook state of the telephone128 is detected (no in step S303), it repeats the determination processin step S303. On the other hand, if the SOC 101 determines that theoff-hook state of the telephone 128 is detected (yes in step S303), theprocess advances to step S304. In step S304, the SOC 101 suspends orsuppresses the output (i.e. the hook detection signal 114) of theoff-hook detection of the telephone 128 by the hook detection circuit117. After that, the process advances to step S305. The suspension orsuppression the off-hook detection output 114 by the hook detectioncircuit 117 continues until a line capture state by the SDAA 104 (linecapture unit 2 106) is released in step S311 to be described later. Thissuspension is executed to prevent the hook detection circuit 117 fromerroneously detecting a hook state due to a change in current because acurrent to the hook detection circuit 117 changes depending on the linecapture state of the SDAA 104.

In step S305, the SOC 101 (first capture control unit) controls the SDAA104 to capture a line using the line capture unit 1 that has DCcharacteristics with an impedance (viewed from the communication line130) sufficiently lower than the telephone 128 (512). After linecapturing starts, the SOC 101 determines in step S306 in FIG. 3B whetheror not a line capture state by the line capture unit 1 becomes stable.In this case, the SOC 101 executes this determination process usinginformation which is associated with the DC characteristics of the linecapture unit 1, and is provided from the SDAA 104. Alternatively, theSOC 101 may execute this determination process by interpreting that theline capture state has become stable when a predetermined period of timeelapses based on a time measured by a timer. If the SOC 101 determinesin step S306 that the line capture state by the line capture unit 1 isnot stable, it repeats the determination process. On the other hand, ifthe SOC 101 determines that the line capture state becomes stable, theprocess advances to step S307.

After the line capture state by the line capture unit 1 becomes stable,the SOC 101 disconnects the line feeding unit 112 from the communicationline 130 using the line feeding circuit connection signal 113 (513) instep S307. The SOC 101 (acting as a connection control unit) connectsthe H-relay 110 to the line side using the H-relay driving signal 111(513) in step S308 such that the external telephone is directlyconnected to the line 130, rather than being connected via the linefeeding circuit 112. As a result, a line current from the communicationline 130 begins to flow toward the telephone 128. However, as describedabove, since the impedance of the line capture unit 1 is set to be lowerthan the telephone 128, most of the line current flows to the linecapture unit 1 side rather than the H-relay 110 side (i.e. the telephone128 side). For this reason, since a current amount flowing toward theH-relay 110 side is very small, an abrupt change in current that flowsto the telephone 128 side upon switching of the H-relay 110 can besuppressed.

In step S309, the SOC 101 (acting as a second capture control unit)controls the SDAA 104 to switch the line capture unit to the linecapture unit 2 106 having DC characteristics with an impedance higherthan the line capture unit 1 105 (out of the plurality of line captureunits 1 to 3 labelled 105, 106 and 107 respectively), thus starting linecapturing (514). With this process, because the impedance of the SDAA104 viewed from the communication line 130 becomes higher, a currentamount which flows to the telephone 128 via the H-relay 110 increasescompared to the case using the line capture unit 1. The impedance of thesecond line capture unit 2 may be slightly less, the same, or more thanthe impedance of the external telephone, as long as a larger portion ofthe current is being transmitted to the external telephone than therewas when the first line capturing unit was connected to thecommunication line 130. Furthermore, the SOC 101 determines in step S310whether or not a line capture state by the line capture unit 2 becomesstable. This process can be implemented by the same process as in stepS306. If the SOC 101 determines that the line capture state is notstable (no in step S310), it repeats the determination process in stepS310. On the other hand, if the SOC 101 determines that the line capturestate does become stable (yes in step S310), the process advances tostep S311.

After the line capture state by the line capture unit 2 becomes stable,the SOC 101 (acting as a line release unit) controls the SDAA 104 to endline capturing by the SDAA 104 so as to release the line capture state(515) in step S311. As a result, since a line current from thecommunication line 130 fully flows to the telephone 128, a currentamount flowing to the telephone 128 further increases. With the aboveprocess, a current amount to the telephone 128 can be prevented fromabruptly increasing upon releasing the line capture state by the SDAA104. After that, the SOC 101 restarts the suspended off-hook detectionof the telephone 128.

<Operation in F/T Mode>

The operation sequence executed when a calling signal (CI signal) fromthe communication line 130 is received in the FAX apparatus 100 duringthe operation in the F/T mode will be described below with reference toFIGS. 4 and 3B. The flowcharts shown in FIGS. 4 and 3B are implementedwhen the CPU of the SOC 101 executes a program in the memory 140.Together with this operation sequence, operation timings will also bedescribed with reference to FIG. 6. FIG. 6 shows a state 601 of thecalling (CI) signal, a state 602 of the SDAA 104, a state 603 of apseudo CI signal, a state 604 of the hook detection signal 114, a state605 of the H-relay 110, and a state 606 of the line feeding circuit 112.A difference with this mode from the no-ringing FAX mode in FIGS. 3A and3B is that a further line-capturing step is incorporated using the linecapture unit 3, so as to communicate with a partner apparatus before anoff-hook state of the telephone 128 is detected after the CI signal isreceived.

When the FAX apparatus 100 shifts to the F/T mode, the SOC 101 connectsthe H-relay 110 to the line feeding circuit 112 side and the linefeeding circuit 112 to the communication line 130 in steps S401 and S402as in steps S301 and S302 in FIG. 3A.

In the FAX apparatus 100 in the F/T mode, the SOC 101 determines in stepS403 whether or not a CI signal is received from the communication line130. If the SOC 101 determines that no CI signal is received, it repeatsthe determination process. On the other hand, if the SOC 101 determinesthat the CI signal is received, the process advances to step S404. Instep S404, the SOC 101 (acting as a third capture control unit) controlsthe SDAA 104 to capture a line using the line capture unit 3 of theplurality of line capture units 1 to 3 labelled 105, 016 and 107respectively (611). After the line is captured, the SOC 101 sends apseudo CI signal from the pseudo CI output circuit 116 to the telephone128 using the pseudo CI driving signal 115 (612, 613) in step S405. Withthis signal, the SOC 101 controls the telephone 128 to ring, therebyinforming the user of call reception. Furthermore, in step S406 the SOC101 outputs a voice message onto the communication line 130. With thisprocess, a voice message indicating that calling the user is in progresscan be transmitted to a partner apparatus which output the CI signal.After that, the process advances to step S407.

The SOC 101 determines in step S407 whether or not the hook detectioncircuit 117 detects an off-hook state of the telephone 128. Thisdetermination process can be implemented by the same process as in stepS303. If the SOC 101 determines that an off-hook state of the telephone128 is not detected, it repeats the determination process in step S407.On the other hand, if the SOC 101 determines that an off-hook state ofthe telephone 128 is detected (614), the process advances to step S408.In step S408, the SOC 101 suspends the output of the off-hook detectionof the telephone 128 by the hook detection circuit 117 (615) as in stepS304. After that, the process advances to step S409.

In order to prevent the VoIP adapter 124 from erroneously recognizing adial pulse or DTMF (dual tone multifrequency) signal input afterhooking, a line is connected to the telephone 128 based on linecapturing operations by the line capture units 1 and 2 as in theprocesses in FIGS. 3A and 3B. In step S409, the SOC 101 controls theSDAA 104 to switch the line capture unit to the line capture unit 1 105having DC characteristics with an impedance lower than the line captureunit 3 107, thereby capturing a line. Since the processes in subsequentsteps S306 to S313 in the F/T mode are the same as those in steps S306to S313 in the no-ringing FAX mode described above, a descriptionthereof will not be repeated.

As described above, when the communication apparatus according to thisembodiment connects the external telephone, which is disconnected fromthe communication line by the H-relay, to the communication line, itcaptures a line using the SDAA 104, which is connected to thecommunication line in parallel to the telephone. More specifically, theSDAA 104 includes the plurality of line capture units having differentimpedances, and captures a line using one of these units. Upon detectionof an off-hook state of the telephone, the SOC captures a line using theline capture unit 1 having an impedance lower than the telephone side,and then switches the H-relay to connect the telephone to thecommunication line. When the FAX apparatus includes the line feedingcircuit connected to the line, the SOC also disconnects that circuitfrom the communication line. With this process, upon disconnecting theline feeding circuit from the communication line, and upon switching theH-relay, the impedance viewed from the communication line can beprevented from becoming a high impedance, thereby suppressing changes ofa current and voltage in the communication line.

Furthermore, the communication apparatus according to this embodimenttemporarily switches a line capture state to the line capture unit 2having a higher impedance than the line capture unit 1 before itreleases the line after the H-relay is switched. With this process,since a current amount flowing to the telephone can be graduallyincreased compared to a case in which the line is immediately released,an unstable change in impedance viewed from the communication line canbe suppressed, thereby suppressing changes of a current and voltage inthe communication line. With the aforementioned processes, thecommunication apparatus according to this embodiment can prevent theadapter that is connected to it from erroneously recognizing a dialpulse.

Upon reception of a call from a partner apparatus 124 via thecommunication line 130, the communication apparatus 100 according tothis embodiment captures a line using the line capture unit 3 107, whichhas an impedance higher than the line capture unit 1 105 and lower thanthe line capture unit 2 106, so as to communicate with the partnerapparatus. After that, upon detection of an off-hook state of thetelephone, the communication apparatus executes the processes using theline capture units 1 and 2, as described above. In this way, the adapterconnected to the communication apparatus can be prevented fromerroneously recognizing a dial pulse or DTMF signal input after hooking(i.e. hanging up) of the telephone.

<First Modification>

The present invention is not limited to the aforementioned embodiment,and allows various modifications. Modifications to be exemplified belowcan obtain the same effects as in the aforementioned embodiment. FIG. 2shows a first modification associated with the FAX apparatus 100according to the aforementioned embodiment. A difference between the FAXapparatuses 100 shown in FIGS. 1 and 2 is the respectivepresence/absence of the line feeding circuit 112. In this way, when theFAX apparatus 100 does not include any line feeding circuit 112, hookdetection of the telephone 128 can be attained using a DC power supply131. Note that the pseudo CI output circuit 116 may include a DC outputfunction, and may supply a current to the hook detection circuit 117.

When the FAX apparatus 100 has the arrangement shown in FIG. 2, theoperation sequence shown in FIGS. 3A and 3B are implemented by excludingsteps S302 and S307, and that shown in FIG. 4 is implemented byexcluding step S402 (and S307). Furthermore, in this case, the timingcharts shown in FIGS. 5 and 6 corresponding to FIGS. 3A, 3B and 4correspond to those except for the states 504 and 606 of the linefeeding circuit 112.

<Second Modification>

The embodiment associated with the FAX apparatus 100 shown in FIGS. 1and 2 has explained the case in which the SDAA 104 includes theplurality of line capture units 105 to 107 (line capture units 1 to 3)having different impedances. In that embodiment, in a process ofconnecting the telephone 128, which is externally connected to the FAXapparatus 100, to the communication line 130, the SDAA 104 selectivelyuses one of these line capture units at a time to change a line capturestate under the control of the SOC 101.

However, the present invention is not limited to the case in which theSDAA 104 includes the plurality of different line capture units. Forexample, the SDAA 104 may include an impedance-variable line captureunit. That is, the FAX apparatus 100 according to the secondmodification includes a single line capture unit which can attain DCcharacteristics of different impedances in place of the separate linecapture units 1 to 3. In this case, the SDAA 104 controls a line capturestate by temporally changing the impedance of the line capture unit inaccordance with an impedance change instruction from the SOC 101.

In this modification, the line capture unit included in the SDAA 104 canbe set at three different impedances corresponding to at least those ofthe line capture units 1 to 3 according to the aforementionedembodiment. The line capture unit of this modification can be set atfirst and second impedances as those corresponding to the line captureunits 1 and 2. The line capture unit of this modification is set at thefirst and second impedances in a situation using the line capture units1 and 2 in which a line is captured to connect the telephone 128 to thecommunication line 130. As in the above embodiment, the first impedanceis lower than the telephone 128 side when viewed from the communicationline 130, and is, for example, a low impedance of about 150 Ω withrespect to a current of 20 mA. The second impedance is higher than thefirst impedance, and is, for example, a high impedance of about 600 Ωwith respect to a current of 20 mA.

The line capture unit of this modification can be set at a thirdimpedance as that corresponding to the line capture unit 3 of theaforementioned embodiment. The line capture unit of this modification isset at the third impedance in a situation using the line capture unit 3in which the SDAA 104 communicates with a partner apparatus via thecommunication line 130. As in the above embodiment, the third impedanceis higher than the first impedance and is lower than the secondimpedance. The third impedance is, for example, a middle impedance ofabout 300 Ω with respect to a current of 20 mA, which is suited tocommunications.

The operation sequence executed when the external telephone 128 is setin an off-hook state during the operation of the FAX apparatus 100according to this modification in the no-ringing FAX mode is basicallythe same as that shown in FIGS. 3A and 3B. The operation sequenceexecuted when a CI signal is received from the communication line 130during the operation in the F/T mode is basically the same as that shownin FIGS. 4 and 3B. In this modification, the line capture operations bythe line capture units 1 to 3 shown in FIGS. 3A, 3B and 4 can beimplemented by the single line capture unit included in the SDAA 104. Inthis case, the line capture operations respectively performed by theline capture units 1 to 3 may instead be executed when the SDAA 104 setsor changes the impedance of the single line capture unit to the first tothird impedances according to an instruction from the SOC 101.

This modification has explained the case in which the impedance of theline capture unit included in the SDAA 104 is set or changed under thecontrol of the SOC 101, as in the embodiment described using FIGS. 3A,3B and 4. The present invention can be implemented when the SDAA 104sets or changes the impedance of the line capture unit by itselfindependently of the control by the SOC 101, in addition to the case inwhich the SDAA 104 uses the line capture unit under the control of theSOC 101, as described above. In this case, the control by the SOC 101can be simplified. This modification can be combined with the firstmodification described above.

<Third Modification>

As shown in FIGS. 1 and 2, the embodiment and modifications described sofar have explained the case in which the FAX apparatus 100 includes thesilicon DAA (SDAA 104) as a network control unit (NCU) which controlsthe line connection state with respect to the communication line 130.However, the present invention is not limited to the case in which theFAX apparatus 100 includes the SDAA 104 as a network control unit. Aswill be described below as a third modification, the FAX apparatus 100can be implemented as that which includes an NCU which does not use anySDAA 104.

FIG. 7 is a block diagram showing the arrangement of a FAX apparatus 700according to the third modification of the present invention. Comparedto the FAX apparatus 100 shown in FIGS. 1 and 2, the FAX apparatus 700includes an NCU 701 in place of the SDAA 104. Also, a circuit whichcorresponds to the CI detection circuit 108, H-relay 110, hook detectioncircuit 117, and the like included in the FAX apparatus 100 is built inthe NCU 701. The NCU 701 is connected to the modem 102, and also to aconnection terminal 702 to which the communication line 130 is connectedand a connection terminal 703 to which the external telephone 128 isconnected. The connection terminals 702 and 703 respectively have L1 andL2 terminals and T1 and T2 terminals as modular connectors. The NCU 701exchanges control signals, and various kinds of information and messageswith the SOC 101 via a signal line 704 including one or more signallines.

FIG. 8 is a block diagram showing an example of the internal arrangementof the NCU 701 shown in FIG. 7. In the NCU 701, a current detection unit802 is connected to the communication line 130 via the connectionterminal 702. The current detection unit 802 detects an off-hook stateof the telephone 128 by detecting a current flowing from thecommunication line 130 side toward the telephone 128 side via theconnection terminals 702 and 703. Upon detection of the off-hook state,the current detection unit 802 sends a HOOK2 signal indicating thatdetection to the SOC 101. The current detected by the current detectionunit 802 is filtered by an analog output filter 803, and is sent as anANLGIN1 signal to the SOC 101. To the current detection unit 802, aP-relay 804, a line capture unit 805 and a diode bridge 806 areconnected. The P-relay 804 is a circuit for generating dial pulses. Thediode bridge 806 is a bridge circuit used to rectify a signal on thecommunication line 130.

A CML (Connect Modem to Line) relay 807 is a relay circuit required toconnect one of the telephone 128 side and the modem 102 side to thecommunication line 130. When the modem 102 side is connected to thecommunication line 130 by the CML relay 807, a signal from thecommunication line 130 is sent from the CML relay 807 to a chargingfilter 808. The charging filter 808 is a filter used to filter chargingpulses sent from the communication line 130. To the charging filter 808,a semiconductor RET (return) circuit 809 is connected. The semiconductorRET circuit 809 is a circuit required to perform a DC line captureoperation, and operates under the control of the SOC 101 using a DCLIMsignal. The charging filter 808 is also connected to an insulatingtransformer 810. The insulating filter 810 isolates between thecommunication line side and the modem side. To the insulatingtransformer 810, a complex/600-Ω switching circuit 811 is connected. Thecomplex/600-Ω switching circuit 811 is a circuit required to set an ACimpedance at either a 600 Ω terminal or complex terminal according to anIPSEL signal from the SOC 101, and is connected to a 2-line/4-lineconversion circuit 812.

A FAX sending signal Tx sent from the modem 102 to the communicationline 130 is input to the 2-line/4-line conversion circuit 812 whichconverts 2 lines on the communication line 130 side to 4 lines on themodem side. On the other hand, a FAX receiving signal Rx from thecommunication line 130 to the modem 102 is output from the 2-line/4-lineconversion circuit 812 to the modem 102 via an RX filter 813. Note thatthe RX filter removes, from the received FAX signal, frequencies otherthan voice-band frequencies of a voice band ranging from 300 to 3400 Hz.

When the communication line 130 is connected to the telephone side bythe CML filter 807, a tapping transformer 814 detects a FAX signal sentfrom a partner apparatus connected via the communication line 130. Upondetection of the FAX signal, the tapping transformer 814 sends anANLGIN2 signal indicating that detection to the SOC 101.

The line capture unit 805 corresponds to those included in the SDAA 104shown in FIGS. 1 and 2. Note that the line capture unit may include aplurality of line capture units 1 to 3 having different impedances, asshown in FIGS. 1 and 2, or may include a single line capture unit whichcan change an impedance between first to third impedances as in thesecond modification. The line capture unit 805 controls a line capturestate based on a DCLIM2 signal as a control signal sent from the SOC101.

A CI detection circuit 819 corresponds to the CI detection circuit 108shown in FIGS. 1 and 2, and detects a CI signal received from thecommunication line. The CI detection circuit 819 transmits thepresence/absence of detection to the SOC 101 using CI detection signalsCI1 and CI2. Note that a CI impedance switching circuit 820 is aswitching circuit which switches an impedance during CI reception inaccordance with a control signal CII received from the SOC 101.

Hook detection circuits 815 and 817 correspond to the hook detectioncircuit 117 shown in FIGS. 1 and 2, and are detection circuits whichdetect an off-hook state of the telephone 128 when the telephone 128 isconnected to the communication line 130. The hook detection circuits 815and 817 transmit the presence/absence of the off-hook state to the SOC101 respectively using a HOOK2 signal and HOOK1 signal.

An H-relay 816 corresponds to the H-relay 110 shown in FIGS. 1 and 2,and is a relay circuit which switches between a connection state anddisconnection state of the telephone 128, externally connected to theFAX apparatus 700 via the connection terminal 703, with respect to thecommunication line 130. An H-detection relay 818 is a circuit whichsupplies a current from the diode bridge 806 to the hook detectioncircuit 817.

In addition, although not shown in FIG. 8, the FAX apparatus 700 mayinclude a line feeding circuit for driving the hook detection circuits815 and 817. Alternatively, the hook detection circuits 815 and 817 maybe driven using a DC power supply. Although not shown in FIG. 8, the FAXapparatus 700 includes a pseudo CI output circuit as in the FAXapparatus 100.

The operation sequence executed when the external telephone 128 is setin an off-hook state during the operation of the FAX apparatus 700 inthe no-ringing FAX mode, and that executed when a CI signal is receivedfrom the communication line 130 during the operation in the F/T mode arethe same as those shown in FIGS. 3A, 3B and 4. When the line captureunit 805 of the FAX apparatus 700 includes a signal line capture unit inplace of three line capture units 1 to 3, the same operation sequencesas in those of the aforementioned second modification are used. Asdescribed above, the present invention can also be implemented as theFAX apparatus 700 including the NCU 701 that does not use any SDAA 104.

Other Embodiments

Aspects of the present invention can also be realized by a computer of asystem or apparatus (or devices such as a CPU (central processing unit)or MPU (microprocessing unit) that reads out and executes a programrecorded on a memory device to perform the functions of theabove-described embodiment(s), and by a method, the steps of which areperformed by a computer of a system or apparatus by, for example,reading out and executing a program recorded on a memory device toperform the functions of the above-described embodiment(s). For thispurpose, the program is provided to the computer for example via anetwork or from a recording medium of various types serving as thememory device (e.g., computer-readable medium).

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2009-174744, filed Jul. 27, 2009, and No. 2010-122030, filed May 27,2010, which are hereby incorporated by reference herein in theirentirety.

1-8. (canceled)
 9. A communication apparatus, which comprises aconnection unit that an external telephone is connected to, a switchingunit that switches between a connection state in which the externaltelephone is connected to a line and a disconnection state in which theexternal telephone is disconnected from the line, a detection unit thatdetects an off-hook state of the external telephone, and a networkcontrol unit that is connected to the line in parallel to the externaltelephone, and controls a capture state of the line, the apparatuscomprising: a capture control unit that captures, when the detectionunit detects the off-hook state of the external telephone in thedisconnection state, the line using a line capture unit, an impedance ofwhich is lower than the external telephone side, and which is includedin the network control unit; a connection control unit that connects theexternal telephone to the line by switching the switching unit to theconnection state after the line capture unit captures the line; and aline release unit that releases the line captured by the line captureunit after the external telephone is connected to the line.
 10. Theapparatus according to claim 9, further comprising: a line feeding unitthat is connected to the line, and supplies a line current of the lineto the detection unit so as to drive the detection unit, wherein theconnection control unit further disconnects the line feeding unit fromthe line after the line capture unit captures the line.
 11. Theapparatus according to claim 9, wherein in the disconnection state, thedetection unit suppresses detection of the off-hook state of theexternal telephone during a period after the off-hook state of theexternal telephone is detected until the line release unit releases theline captured by the line capture unit.
 12. A communication apparatus,which comprises a connection unit that an external telephone isconnected to, a switching unit that switches between a connection statein which the external telephone is connected to a line and adisconnection state in which the external telephone is disconnected fromthe line, a detection unit that detects an off-hook state of theexternal telephone, and a network control unit that is connected to theline in parallel to the external telephone, and controls a capture stateof the line, the apparatus comprising: a capture control unit that sets,when the detection unit detects the off-hook state of the externaltelephone in the disconnection state, an impedance of a line captureunit included in the network control unit to be an impedance lower thanthe external telephone side, and captures the line using the linecapture unit; a connection control unit that connects the externaltelephone to the line by switching the switching unit to the connectionstate after the line capture unit of the set impedance captures theline; and a line release unit that releases the line captured by theline capture unit after external telephone is connected to the line. 13.A control method of a communication apparatus, which comprises aconnection unit that an external telephone is connected to, a switchingunit that switches between a connection state in which the externaltelephone is connected to a line and a disconnection state in which theexternal telephone is disconnected from the line, a detection unit thatdetects an off-hook state of the external telephone, and a networkcontrol unit that is connected to the line in parallel to the externaltelephone, and controls a capture state of the line, the methodcomprising: controlling a capture control unit to capture, when thedetection unit detects the off-hook state of the external telephone inthe disconnection state, the line using a line capture unit, animpedance of which is lower than the external telephone side, and whichis included in the network control unit; controlling a connectioncontrol unit to connect the external telephone to the line by switchingthe switching unit to the connection state after the line capture unitcaptures the line; and controlling a line release unit to release theline captured by the line capture unit after the external telephone isconnected to the line.
 14. The control method according to claim 13,further comprising: controlling a line feeding unit that is connected tothe line to supply a line current of the line to the detection unit soas to drive the detection unit, and controlling the connection controlunit to disconnect the line feeding unit from the line after the linecapture unit captures the line.
 15. The control method according toclaim 13, further comprising controlling, in the disconnection state,the detection unit to suppress detection of the off-hook state of theexternal telephone during a period after the off-hook state of theexternal telephone is detected until the line release unit releases theline captured by the second line capture unit.
 16. A control method of acommunication apparatus, which comprises a connection unit that anexternal telephone is connected to, a switching unit that switchesbetween a connection state in which the external telephone is connectedto a line and a disconnection state in which the external telephone isdisconnected from the line, a detection unit that detects an off-hookstate of the external telephone, and a network control unit that isconnected to the line in parallel to the external telephone, andcontrols a capture state of the line, the method comprising: controllinga capture control unit to set, when the detection unit detects theoff-hook state of the external telephone in the disconnection state, animpedance of a line capture unit included in the network control unit tobe an impedance lower than the external telephone side, and to capturethe line using the line capture unit; controlling a connection controlunit to connect the external telephone to the line by switching theswitching unit to the connection state after the line capture unit ofthe set impedance captures the line; and controlling a line release unitto release the line by the captured line capture unit after the externaltelephone is connected to the line.